1. Field of the Invention
This invention relates generally to a method and apparatus for determining which of a given set of known reference patterns is the closest match to a particular unknown pattern, and more particularly, to a method and apparatus whereby the Fourier Transform of both the reference pattern and the unknown pattern are computed, corrections are made, and the comparison is used to determine which of the group of known reference patterns is the "best match" for the unknown pattern.
2. Description of Prior Art
The prior art has used many types of systems in an attempt to identify unknown machine-readable characters as being particular ones of a known set of reference characters. For example, in reading magnetic ink character recognition signals (MICR) from MICR-encoded banking documents and the like, the unknown MICR character is scanned and then an equivalent analog electrical signal is generated. This analog electrical signal is digitized and can be stored in a memory for future comparison purposes. The criteria for comparison in the prior art are varied, and many techniques involve the use of a weighted specification reference system, a binary dot scan system, or the potential use of a Haddamard Matrix transform approach for converting both the unknown character and the group of known reference characters prior to attempting to identify a "best match". These systems are either extremely complex, or have an unacceptably low recognition probability, or require extensive processing equipment to perform the mathematical calculations and transforms involved, and hence they are not suitable for reliable, high speed, low cost operations.
Historically, wave form pattern recognition has been accomplished through three primary approaches in the prior art. The first approach is still used in many areas today and is strictly a manual or human recognition system. The second approach in general use today utilizes a specification reference system embodying an inductive delay line which allows a time-based comparison of multiple peak amplitudes referenced to specific peak amplitudes that specify time basis. The third automated approach involves the use of a binary-grid comparison system embodying a linear array of sensors which scan the target signature or pattern to be identified and then time-framed. The presence or absence of signals above a certain threshold determine the pattern, and this pattern is compared statistically to a reference pattern or to a set of reference patterns.
Additionally, Fourier Transforms have been used for signal enhancement in reconnaissance mapping where sensors are used to scan patterns in order to find strong signals at critical spectrum points; and, these isolated signals are then amplified and fed back to enhance the original pattern, but a pattern recognition extension has never been derived from this concept let alone on a commercial basis. Another method used for map enhancement and target discrimination is the Hadamard Transform approach.